The invention relates to a projection exposure apparatus having several parallelly arranged objectives and a scanning method for microlithographically exposing large-area structures.
Projection exposure apparatus and scanning methods of the above kind are disclosed in Japanese patent publications JP 7-057 986, JP 7-135 165 and JP 7-218 863.
In all of these systems, an imaging scale of 1:1 is selected as, for example, in JP 7-135 165, paragraph 15, this imaging scale is provided for the condition that the mask and exposed plate can be interconnected during scanning. While this publication discloses lens systems as projection objectives, the other two Japanese publications disclose catadioptric projection objectives of the Dyson or Offner type.
Five to seven systems, which operate in parallel, are each provided with their own light sources and illuminating optics. The systems exhibit polygons as individual image fields (in two offset lines) which ensure a uniform line by line exposure during scanning.
No polygonal cropping of the optics is provided in the lens systems of Japanese patent publication JP 7-135 165. The deflecting mirrors of the catadioptric objectives are shown rectangular in the other two publications but have no reference to the trapezoidal-shaped or hexagonal image fields. In this technology having 1:1 imaging, very large format masks are required.
Systems of this kind are also known in European patent publication 0,723,173 and U.S. Pat. Nos. 5,614,988; 5,688,624; 5,617,211; and, 5,617,181.
The microlithography for semiconductor manufacture typically works with wafer steppers having objectives with demagnifying imaging of a factor of 4 or 5 with an image field of approximately 30 mm diameter with structural widths of 0.3 to 0.5 xcexcm. Scanners increase the ratio of image field length to image field width.
For flat panel displays as in the LCD technology, large interconnected structured areas having a more than 10 inch diagonal for structure widths of typically 3 xcexcm are required. The image fields of conventional stepper objectives are far too small. Unacceptable disturbance locations at the transitions between the exposing zones (stitching) would result in accordance with the step method and the repeat method of the wafer steppers.
European patent publication 0,744,665 discloses an arrangement for exposing a complete flat panel display (FPD) at once with a magnifying objective having a non-rotational symmetrical element.
It is an object of the invention to provide an alternative technology for the photolithographic manufacture of large-area structures. Preferably, masks should be used which correspond to those used for microchips.
The projection exposure apparatus of the invention includes: a plurality of objectives arranged in parallel with each other; and, the objectives being configured to magnify.
According to the above, it is a feature of the invention to introduce magnifying projection objectives into an objective array.
The structural widths, which are necessary for a flat panel display are relatively large compared to the state of the art for the manufacture of microchips. Accordingly, it is not difficult to provide masks having smaller structural widths than in the product. An area reduction of the mask is achieved thereby in the quadratic ratio which makes it substantially easier to manufacture and manipulate the masks.
The scanning with different speed of mask and wafer has been investigated for the manufacture of microchips with a far greater accuracy than required for flat panel displays.
The invention proceeds from the realization that:
(a) a significant simplification of the entire process is provided when the masks (reticles) are used from established technology of microchip manufacture with the conventional size and structural width; and,
(b) it is known from the demagnifying scanning technology of the microchip manufacture (even for very tight tolerances) to synchronously move reticle and wafer at different speeds.
According to another feature of the invention, each objective is provided with its own object mask (reticle).
Separate reticles for each objective make possible simpler controllable small reticles which can be controllably adjusted during operation.
According to another feature of the invention, each objective is assigned its own illuminating device and each illuminating device is provided with a separate light source. The quality of the illumination and the power of the arrangement (high throughput) is optimized by the parallel arrangement of several illuminating optics and several light sources.
According to still another feature of the invention, one or several frames of each objective is cut in a polygonal form and one or more lenses of each objective is (are) configured to have a polygonal form. The image field of each objective has a polygonal form and the above adaptation of the frames and lenses of the objective to the polygonal form of the lens permits a very compact configuration of the objective array and therefore a very stable and effective strip-by-strip scan exposure. The objective can be a pure lens objective and the use thereof utilizes established optical design and permits compact packing of the individual elements of the array such as in more than two parallelly offset rows.
The objectives can have an intermediate image and permit arrangements having a one-part reticle.
The primary area of application of the apparatus and method of the invention is for the manufacture of flat panel display structures.